Fluidized bed coking with fuel gas production

ABSTRACT

A Flexicoking™ unit which retains the capability of converting heavy oil feeds to lower boiling liquid hydrocarbon products while making a fuel gas from rejected coke to provide only a minimal coke yield. The heater section of the conventional three section unit (reactor, heater, gasifier) is eliminated and the cold coke from the reactor is passed directly to the gasifier which is modified by the installation of separators to remove coke particles from the product gas which is taken out of the gasifier for ultization. Hot coke from the gasifier is passed directly to the coking zone of the reactor to supply heat to support the endothermic cracking reactions and supply seed nuclei for the formation of coke in the reactor. Coke is withdrawn from the gasifier to remove excess coke and to purge the system of metals and ash.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/014,762 filed Jun. 20, 2014, herein incorporated by reference inits entirety.

FIELD OF THE INVENTION

This invention relates to a fluid coking process in which a heavy oilfeed is subjected to thermal cracking (coking) in a fluidized bedreactor with the coke product being converted by gasification to form afuel gas.

BACKGROUND OF THE INVENTION

Heavy petroleum oils and residual fractions derived from them arecharacterized by a combination of properties which may be summarized ashigh initial boiling point, high molecular weight and low hydrogencontent relative to lower boiling fractions such as naphtha, gasoline,and distillates; frequently these heavy oils and high boiling fractionsexhibit high density (low API gravity), high viscosity, high carbonresidue, high nitrogen content, high sulfur content, and high metalscontent.

Technologies for upgrading heavy petroleum feedstocks can be broadlydivided into carbon rejection and hydrogen addition processes. Carbonrejection redistributes hydrogen among the various components, resultingin fractions with increased H/C atomic ratios and products includingfractions with lower H/C atomic ratios and solid coke-like materials.Hydrogen addition processes, by contrast, involve reaction of heavycrude oils with an external source of hydrogen and result in an overallincrease in H/C ratio.

Carbon rejection processes generally operate at moderate to hightemperatures and low pressures and suffer from a lower liquid yield oftransportation fuels than hydrogen addition processes, because a largefraction of the feedstock is rejected as solid coke; light gases arealso formed as by-products in the thermal cracking reactions and, beingof high H/C ratio tend to degrade the quantity of the more valuableliquid products. The liquids are generally of poor quality and mustnormally be hydrotreated before they can be used as feeds for catalyticprocesses to make transportation fuels.

Thermal cracking processes include those such as visbreaking whichoperate under relatively mild conditions and are intended mainly toincrease the yields of distillates from residual fractions. Cokingprocesses, by contrast, operate at significantly higher severities andproduce substantial quantities of coke as the by-product; the amount ofthe coke is typically of the order of one-third the weight of the feed.The main coking processes now in use are delayed coking, fluid cokingand its variant, Flexicoking™. The present invention is concerned withFlexicoking.

Fluidized bed coking is a petroleum refining process in which heavypetroleum feeds, typically the non-distillable residues (resids) fromthe fractionation of heavy oils are converted to lighter, more usefulproducts by thermal decomposition (coking) at elevated reactiontemperatures, typically about 480 to 590° C., (about 900 to 1100° F.)and in most cases from 500 to 550° C. (about 930 to 1020° F.). Heavyoils which may be processed by the fluid coking process include heavyatmospheric resids, petroleum vacuum distillation bottoms, aromaticextracts, asphalts, and bitumens from tar sands, tar pits and pitchlakes of Canada (Athabasca, Alta.), Trinidad, Southern California (LaBrea (Los Angeles), McKittrick (Bakersfield, Calif.), Carpinteria (SantaBarbara County, Calif.), Lake Bermudez (Venezuela) and similar depositssuch as those found in Texas, Peru, Iran, Russia and Poland.

The process is carried out in a unit with a large reactor containing hotcoke particles which are maintained in the fluidized condition at therequired reaction temperature with steam injected at the bottom of thevessel with the average direction of movement of the coke particlesbeing downwards through the bed. The heavy oil feed is heated to apumpable temperature, typically in the range of 350 to 400° C. (about660 to 750° F.) mixed with atomizing steam, and fed through multiplefeed nozzles arranged at several successive levels in the reactor. Steamis injected into a stripping section at the bottom of the reactor andpasses upwards through the coke particles descending through the densephase of the fluid bed in the main part of the reactor above thestripping section. Part of the feed liquid coats the coke particles inthe fluidized bed and is subsequently cracked into layers of solid cokeand lighter products which evolve as gas or vaporized liquid. Reactorpressure is relatively low in order to favor vaporization of thehydrocarbon vapors which pass upwards from dense phase into dilute phaseof the fluid bed in the coking zone and into cyclones at the top of thecoking zone where most of the entrained solids are separated from thegas phase by centrifugal force in one or more cyclones and returned tothe dense fluidized bed by gravity through the cyclone diplegs. Themixture of steam and hydrocarbon vapors from the reactor is subsequentlydischarged from the cyclone gas outlets into a scrubber section in aplenum located above the coking zone and separated from it by apartition. It is quenched in the scrubber section by contact with liquiddescending over sheds, A pumparound loop circulates condensed liquid toan external cooler and back to the top shed row of the scrubber sectionto provide cooling for the quench and condensation of the heaviestfraction of the liquid product. This heavy fraction is typicallyrecycled to extinction by feeding back to the coking zone in thereactor.

The coke particles formed in the coking zone pass downwards in thereactor and leave the bottom of the reactor vessel through a strippersection where they are exposed to steam in order to remove occludedhydrocarbons. The solid coke from the reactor, consisting mainly ofcarbon with lesser amounts of hydrogen, sulfur, nitrogen, and traces ofvanadium, nickel, iron, and other elements derived from the feed, passesthrough the stripper and out of the reactor vessel to a burner or heaterwhere it is partly burned in a fluidized bed with air to raise itstemperature from about 480 to 700° C. (about 900° to 1300° F.) to supplythe heat required for the endothermic coking reactions, after which aportion of the hot coke particles is recirculated to the fluidized bedreaction zone to transfer the heat to the reactor and to act as nucleifor the coke formation. The balance is withdrawn as coke product. Thenet coke yield is only about 65 percent of that produced by delayedcoking.

The Flexicoking™ process, also developed by Exxon Research andEngineering Company, is, in fact, a variant of the fluid coking processthat is operated in a unit including a reactor and a heater, but alsoincluding a gasifier for gasifying the coke product by reaction with anair/steam mixture to form a low heating value fuel gas. A stream of cokepasses from the heater to the gasifier where all but a small fraction ofthe coke is gasified to a low-Btu gas (˜120 Btu/standard cubic feet) bythe addition of steam and air in a fluidized bed in an oxygen-deficientenvironment to form fuel gas comprising carbon monoxide and hydrogen.The fuel gas product from the gasifier, containing entrained cokeparticles, is returned to the heater to provide most of the heatrequired for thermal cracking in the reactor with the balance of thereactor heat requirement supplied by combustion in the heater. A smallamount of net coke (about 1 percent of feed) is withdrawn from theheater to purge the system of metals and ash. The liquid yield andproperties are comparable to those from fluid coking. The fuel gasproduct (Flexigas) is withdrawn from the heater following separation ininternal cyclones which return coke particles through their diplegs.

The Flexicoking process is described in patents of Exxon Research andEngineering Company, including, for example, U.S. Pat. No. 3,661,543(Saxton), U.S. Pat. No. 3,759,676 (Lahn), U.S. Pat. No. 3,816,084(Moser), U.S. Pat. No. 3,702,516 (Luckenbach), U.S. Pat. No. 4,269,696(Metrailer). A variant is described in U.S. Pat. No. 4,213,848 (Saxton)in which the heat requirement of the reactor coking zone is satisfied byintroducing a stream of light hydrocarbons from the product fractionatorinto the reactor instead of the stream of hot coke particles from theheater. Another variant is described in U.S. Pat. No. 5,472,596 (Kerby)using a stream of light paraffins injected into the hot coke return lineto generate olefins. Early work proposed units with a stackedconfiguration but later units have migrated to a side-by-sidearrangement.

While the unit configuration using the separate reactor, heater andgasifier has demonstrated its capabilities and potential in a number ofoperating units providing an attractive return on capital, it wouldnaturally be desirable to reduce capital cost in order to improve thereturn.

SUMMARY OF THE INVENTION

We have now devised a new form of Flexicoking unit which retains thecapability of converting heavy oil feeds to lower boiling liquidhydrocarbon products with only a minimal coke yield but which can beconstructed with a lower capital expenditure. in the present invention,the heater of the conventional three section unit (reactor, heater,gasifier) is eliminated and the cold coke from the reactor is passeddirectly to the gasifier which is modified by the installation ofinternal or external cyclones to separate coke particles from theproduct gas which is taken out of the gasifier via the gas outlets ofthe cyclones. Hot coke from the gasifier is passed directly to thecoking zone of the reactor to supply heat to support the endothermiccracking reactions and supply seed nuclei for the formation of coke inthe reactor. Coke is withdrawn from the gasifier to remove excess cokeand to purge the system of metals and ash.

According to the present invention, the coking process for converting aheavy hydrocarbon feedstock to lower boiling products performed in afluid coking process unit including a fluid coking reactor and agasification reactor (gasifier), comprises: (i) introducing the heavyhydrocarbon feedstock into the coking zone of a fluid coking reactorcontaining a fluidized bed of solid particles maintained at cokingtemperatures to produce a vapor phase product including normally liquidhydrocarbons, while coke is deposited on the solid particles; (ii)passing the solid particles, with coke deposited on them to thegasifier, (iii) contacting the solid particles with coke deposited onthem in the gasifier with steam and an oxygen-containing gas, typicallyair or oxygen-enriched air, in an oxygen limited atmosphere at anelevated temperature to heat the solid particles and form a fuel gasproduct comprising carbon monoxide and hydrogen, (iv) recycling theheated solid particles from the gasifier to the coking zone to supplyheat to the coking zone.

The solid particles are normally composed only of coke and for thatreason will be referred to as coke particles even though otherparticulate solids may be used as the circulating heat transfer mediumso that coke becomes deposited on them in the reactor and removed in thegasification reaction in the separate gasifier vessel. The heat requiredto sustain the cracking reactions is supplied by the exothermicreactions taking place in the gasifier and this heat is transferred tothe reactor by the transport of the partly gasified particles from thegasifier to the reactor. In the present invention, the coke particlesare passed directly to the gasifier from the coking reactor signifyingthat they are transferred to the gasifier without passing through anintermediate heater and that they are recirculated directly from thegasifier to the coking reactor again without passing through a heater.

The modified coking unit according to the present invention comprises:(i) a fluid coking reactor with an inlet for a heavy hydrocarbonfeedstock, an outlet for cracked hydrocarbon vapors at the top of thereactor, an inlet at the bottom of the reactor for a fluidizing gas, aninlet for heated solid particles and a solid particle outlet at thebottom of the reactor for solid particles with coke deposited on them,(ii) a gasifier with an inlet for steam and oxygen-containing gas at itsbottom, a solid particle inlet for solid particles with coke depositedon them (e.g., at the side of the vessel at the dense bed/dilute phaseinterface), an outlet for fuel gas at its top and a solid particleoutlet for solid particles heated in the gasifier (e.g., at anotherlocation on the side of the vessel at the dense bed/dilute phaseinterface), (iii) a transfer line for passing the solid particles withcoke deposited on them from the solid particle outlet directly to thesolid particle inlet of the gasifier, (iv) a transfer line for passingthe solid particles heated in the gasifier from the solid particleoutlet of the gasifier to the solid particle inlet of the reactor forrecycling the heated solid particles from the gasifier to the reactor tosupply heat to the coking zone of the reactor.

DRAWINGS

In the accompanying drawings:

FIG. 1A is a simplified scheme of a three-vessel side-by-sideFlexicoking unit comprising reactor, heater and gasifier;

FIG. 1B is a simplified scheme of a two-vessel side-by-side Flexicokingunit comprising reactor and gasifier;

FIG. 2 is a simplified scheme of a side-by-side Flexicoking unitcomprising reactor directly connected to a gasifier with a solidsseparator external to the gasifier.

DETAILED DESCRIPTION

In this description, the term “Flexicoking” (trademark of ExxonMobilResearch and Engineering Company) is used to designate the fluid cokingprocess in which heavy petroleum feeds are subjected to thermal crackingin a fluidized bed of heated solid particles to produce hydrocarbons oflower molecular weight and boiling point along with coke as a by-productwhich is deposited on the solid particles in the fluidized bed, the cokeis then converted to a fuel gas by contact at elevated temperature withsteam and an oxygen-containing gas in a gasification reactor (gasifier).

FIG. 1A shows a Flexicoker unit with its characteristic three reactionvessels—reactor, heater and gasifier—in side-by-side arrangement;although the footprint of the side-by-side arrangement is larger thanthat of the stacked units shown in U.S. Pat. No. 3,661,543 and U.S. Pat.No. 3,816,084, it is less subject to upsets and potential equipmentfailures as noted in U.S. Pat. No. 3,759,676 and has now becomeconventional.

The unit comprises reactor section 10 with the coking zone and itsassociated stripping and scrubbing sections (not separately indicated asconventional), heater section 11 and gasifier section 12. Therelationship of the coking zone, scrubbing zone and stripping zone inthe reactor section is shown, for example, in U.S. Pat. No. 5,472,596,to which reference is made for a description of the Flexicoking unit andits reactor section. A heavy oil feed is introduced into the unit byline 13 and cracked hydrocarbon product withdrawn through line 14.Fluidizing and stripping steam is supplied by line 15. Cold coke istaken out from the stripping section at the base of reactor 10 by meansof line 16 and passed to heater 11. The term “cold” as applied to thetemperature of the withdrawn coke is, of course, decidedly relativesince it is well above ambient at the operating temperature of thestripping section. Hot coke is circulated from heater 11 to reactor 10through line 17. Coke from heater 11 is transferred to gasifier 12through line 21 and hot, partly gasified particles of coke arecirculated from the gasifier back to the heater through line 22. Theexcess coke is withdrawn from the heater 11 by way of line 23. Gasifier12 is provided with its supply of steam and air by line 24 and hot fuelgas is taken from the gasifier to the heater though line 25. The lowenergy fuel gas is taken out from the unit through line 26 on theheater; coke fines are removed from the fuel gas in heater cyclonesystem 27 comprising serially connected primary and secondary cycloneswith diplegs which return the separated fines to the fluid bed in theheater.

FIG. 1B shows the modified unit consisting essentially of reactor 30which is constructed and operated in the same manner as reactor 10 withfluidizing/stripping steam supplied through line 33 and crackedhydrocarbon products taken out through line 34. Cold coke is transferreddirectly from reactor 30 to gasifier 31 through line 35 and hot, partlygasified coke particles are transferred directly from gasifier 31 toreactor 30 by way of line 36 to provide the heat required for thecracking reactions in the coking zone of the reactor. Steam and airenter the gasifier from line 37 and the low energy fuel gas leaves thegasifier through line 38; coke fines are removed from the fuel gas ingasifier in cyclone system 39 comprising serially connected primary andsecondary cyclones with diplegs which return the separated fines to thefluid bed in the gasifier. Coke may be purged from the gasifier asneeded through line CP.

In many respects the Flexicoking unit of the present invention resemblesthe known type of three-vessel Flexicoker and the operating parameterswill be similar in many respects.

In particular, the reactor will be operated according to the parametersnecessary for the required coking processes. Thus, the heavy oil feedwill typically be a heavy (high boiling) reduced petroleum crude;petroleum atmospheric distillation bottoms; petroleum vacuumdistillation bottoms, or residuum; pitch; asphalt; bitumen; other heavyhydrocarbon residues; tar sand oil; shale oil; or even a coal slurry orcoal liquefaction product such as coal liquefaction bottoms. Such feedswill typically have a Conradson Carbon Residue (ASTM D189-165) of atleast 5 wt. %, generally from about 5 to 50 wt. %. Preferably, the feedis a petroleum vacuum residuum.

A typical petroleum chargestock suitable for the practice of the presentinvention will have the composition and properties within the ranges setforth below.

Conradson Carbon 5 to 40 wt. % API Gravity −10 to 35° Boiling Point 340°C.+ to 650° C.+ Sulfur 1.5 to 8 wt. % Hydrogen 9 to 11 wt. % Nitrogen0.2 to 2 wt. % Carbon 80 to 86 wt. % Metals 1 to 2000 wppm

The heavy oil feed, pre-heated to a temperature at which it is flowableand pumpable, is introduced into the coking reactor towards the top ofthe reactor vessel through injection nozzles which are constructed toproduce a spray of the feed into the bed of fluidized coke particles inthe vessel. Temperatures in the coking zone of the reactor are typicallyin the range of about 450 to 850° C. and pressures are kept at arelatively low level, typically in the range of about 120 to 400 kPag(about 17 to 58 psig), and most usually from about 200 to 350 kPag(about 29 to 51 psig), in order to facilitate fast drying of the cokeparticles, preventing the formation of sticky, adherent high molecularweight hydrocarbon deposits on the particles which could lead to reactorfouling. The light hydrocarbon products of the coking (thermal cracking)reactions vaporize, mix with the fluidizing steam and pass upwardlythrough the dense phase of the fluidized bed into a dilute phase zoneabove the dense fluidized bed of coke particles. This mixture ofvaporized hydrocarbon products formed in the coking reactions flowsupwardly through the dilute phase with the steam at superficialvelocities of about 1 to 2 metres per second (about 3 to 6 feet persecond), entraining some fine solid particles of coke which areseparated from the cracking vapors in the reactor cyclones as describedabove. The cracked hydrocarbon vapors pass out of the cyclones into thescrubbing section of the reactor and then to product fractionation andrecovery.

As the cracking process proceeds in the reactor, the coke particles passdownwardly through the coking zone, through the stripping zone, whereoccluded hydrocarbons are stripped off by the ascending current offluidizing gas (steam). They then exit the coking reactor and pass tothe gasification reactor (gasifier) which contains a fluidized bed ofsolid particles and which operates at a temperature higher than that ofthe reactor coking zone. in the gasifier, the coke particles areconverted by reaction at the elevated temperature with steam and anoxygen-containing gas into a low energy content fuel gas comprisingcarbon monoxide and hydrogen.

The gasification zone is typically maintained at a high temperatureranging from about 850 to 1000° C. (about 1560 to 1830° F.) and apressure ranging from about about 0 to 1000 kPag (about 0 to about 150psig), preferably from about 200 to 400 kPag (about 30 to 60 psig).Steam and an oxygen-containing gas such as air, commercial oxygen or airmixed with oxygen are passed into the gasifier for reaction with thesolid particles comprising coke deposited on them in the coking zone. Inthe gasification zone the reaction between the coke and the steam andthe oxygen-containing gas produces a hydrogen and carbonmonoxide-containing fuel gas and a partially gasified residual cokeproduct and conditions in the gasifier are selected accordingly. Steamand air rates will depend upon the rate at which cold coke enters fromthe reactor and to a lesser extent upon the composition of the cokewhich, in turn will vary according to the composition of the heavy oilfeed and the severity of the cracking conditions in the reactor withthese being selected according to the feed and the range of liquidproducts which is required. The fuel gas product from the gasifier maycontain entrained coke solids and these are removed by cyclones or otherseparation techniques in the gasifier section of the unit; cyclones maybe internal cyclones in the main gasifier vessel itself or external in aseparate, smaller vessel as described below. The fuel gas product istaken out as overhead from the gasifier cyclones. The resulting partlygasified solids are removed from the gasifier and introduced directlyinto the coking zone of the coking reactor at a level in the dilutephase above the lower dense phase.

In the present invention, the cold coke from the reactor is transferreddirectly to the gasifier; this transfer, in almost all cases will beunequivocally direct with one end of the tubular transfer line connectedto the coke outlet of the reactor and its other end connected to thecoke inlet of the gasifier with no intervening reaction vessel, i.e.heater. The presence of devices other than the heater is not however tobe excluded, e.g. inlets for lift gas etc. Similarly, while the hot,partly gasified coke particles from the gasifier are returned directlyfrom the gasifier to the reactor this signifies only that there is to beno intervening heater as in the conventional three-vessel Flexicoker butthat other devices may be present between the gasifier and the reactor,e.g. gas lift inlets and outlets. In the two-vessel unit shown in FIG.1B, the partly gasified coke fines are separated from the fuel gas bythe cyclones internal to the gasifier and the hot coke particlesconveyed from the gasifier straight to the reactor. FIG. 2 shows a unitin which the gasifier section in which the cyclones for separating thecoke fines from the fuel gas are installed in a smaller separator vesselexternal to the main gasifier vessel. In this unit comprising reactor40, main gasifier vessel 41 and separator 42, the heavy oil feed isintroduced into reactor 40 through line 43 and fluidizing/stripping gasthrough line 44; cracked hydrocarbon products are taken out through line45. Cold, stripped coke is routed directly from reactor 40 to gasifier41 by way of line 46 and hot coke returned to the reactor in line 47.Steam and air are supplied through line 48. In this case, the fuel gasproduced in the gasifier is not taken directly from the gasifier as inFIG. 1B but, instead the flow of gas containing coke fines is routed toseparator vessel 42 through line 49 which is connected to a gas outletof the main gasifier vessel 41. The fines are separated from the gasflow in cyclone system 50 comprising serially connected primary andsecondary cyclones with diplegs which return the separated fines to theseparator vessel. The separated fines are then returned to the maingasifier vessel through return line 51 and the fuel gas product takenout by way of line 52. Coke is purged from the separator through line53.

As an alternative to the use of cyclones to effect separation of thecoke fines from the fuel gas sintered porous metal/ceramic solids/gasfillers offer advantages in the high temperature environments of themain gasifier vessel or the adjacent separator vessel. Sintered metalfilters can be operated at temperatures up to about 900° C. (about 1650°F.) while ceramic filters can be used up to about 980° C. (about 1800°F.), While provision has to be made for removal of the fines from thefilters using a suitable blowback gas with collection of the fines,these systems are well established, commercially available and can beadapted to use in the present units. In them, sintered metal or ceramicfilter dements with sufficiently small pores, and sized at anappropriate gas flux rate, retain the coke solids at the filter surface.The cake of solids is dislodged at a predetermined pressure drop (afunction of cake thickness and compressibility) by initiating a reverseflow of gas and the dislodged solids are purged from the filter system.They may be returned directly to the gasifier for reuse or purged fromthe system and sent to a storage or collection unit.

Gas-solid filtration systems with blowback gas eliminate the need toscrub the fuel gas to remove the solid particles because the efficiencyis typically 99.99% on solids removal. The only additional need forusing such separation methodology is a high-pressure blow-back gas atcirca (1.8-2.0)×(the prevailing process pressure) but since the unitsoperate at relatively low pressure, provision of appropriate blowback isno significant issue; high pressure nitrogen, for example is generallysuitable for use as blow back gas with filters in the gasifier sectionand is fully compatible with the general process environment andconditions. The compressed fuel gas from the unit or compressed CO₂ arealternative sources of blowback gas.

For high loadings, however, cyclones have the advantage of limitedinvestment and only some pressure drop to remove the coarsest particles.For this reason it may be desirable to utilize cyclones (withprimary/secondary cyclone stages) for an initial separation followed byfilters to replace a tertiary cyclone/venturi scrubber departiculationstage.

1. A coking process for converting a heavy hydrocarbon feedstock tolower boiling products in a fluid coking process unit comprised of afluid coking reactor and a gasifier, comprising: (i) introducing theheavy hydrocarbon feedstock into the coking zone of a fluid cokingreactor containing a fluidized bed of solid particles maintained atcoking temperatures to produce a vapor phase product including normallyliquid hydrocarbons, while coke is deposited on the solid particles;(ii) passing the solid particles, with coke deposited on them directlyto the gasifier, (iii) contacting the solid particles with cokedeposited on them in the gasifier with steam and an oxygen-containinggas in an oxygen limited atmosphere at an elevated temperature to heatthe solid particles and form a fuel gas product from the coke,comprising carbon monoxide and hydrogen, (iv) recycling the heated solidparticles directly from the gasifier to the coking zone to supply heatto the coking zone.
 2. A process according to claim 1 in which theoxygen-containing gas comprises air or oxygen-enriched air.
 3. A fluidcoking unit for converting a heavy hydrocarbon feedstock to lowerboiling products and for producing a fuel gas product in a fluid cokingprocess unit comprised of a fluid coking reactor section and a gasifiersection, comprising: (i) a fluid coking reactor section with an inletfor a heavy hydrocarbon feedstock, an outlet for cracked hydrocarbonvapors at the top of the reactor, an inlet at the bottom of the reactorfor a fluidizing gas, an inlet for heated solid particles and a solidparticle outlet at the bottom of the reactor for solid particles withcoke deposited on them, (ii) a gasifier section with an inlet for steamand oxygen-containing gas at its bottom, a solid particle inlet forsolid particles with coke deposited on them, an outlet for fuel gas atits top and a solid particle outlet for solid particles heated in thegasifier, (iii) a transfer line for passing the solid particles withcoke deposited on them from the reactor solid particle outlet directlyto the solid particle inlet of the gasifier section, (iv) a transferline for passing the solid particles heated in the gasifier section fromthe solid particle outlet of the gasifier section to the solid particleinlet of the reactor section for recycling the heated solid particlesfrom the gasifier section to the reactor section to supply heat to thecoking zone of the reactor.
 4. A fluid coking unit according to claim 3in which the gasifier section includes a gasifier vessel having internalcyclones to separate solid particles heated in the gasifier from thefuel gas.
 5. A fluid coking unit according to claim 3 in which thegasifier section includes a gasifier vessel in which the solid particleswith coke deposited on them are contacted with the steam andoxygen-containing gas and internal cyclones for separating solidparticles heated in the gasifier from the fuel gas.
 6. A fluid cokingunit according to claim 3 in which the gasifier section includes (i) agasifier vessel in which the solid particles with coke deposited on themare contacted with the steam and oxygen-containing gas and (ii) aseparator in which solid particles heated in the gasifier vessel areseparated from the fuel gas.
 7. A fluid coking unit according to claim 6in which the separator vessel includes cyclones for separating solidparticles heated in the gasifier vessel from the fuel gas.
 8. A fluidcoking unit according to claim 6 in which the separator vessel includesgas/solid filters for separating solid particles heated in the gasifiervessel from the fuel gas.
 9. A fluid coking unit according to claim 8 inwhich the gas/solid filters for separating solid particles heated in thegasifier vessel from the fuel gas comprise porous ceramic filters,sintered metal filters or a combination thereof.
 10. A fluid coking unitaccording to claim 3 in which the gasifier section includes a maingasifier vessel in which the solid particles from the reactor with cokedeposited on them are contacted with the steam and oxygen-containing gasto form fuel gas and a separator vessel having (i) a gas inlet connectedto the main gasifier vessel, (ii) cyclones for separating solidparticles heated in the main gasifier vessel from the fuel gas and (iii)a solid particle return line connecting the separator vessel to the maingasifier vessel for returning separated solid particles to the maingasifier vessel.
 11. A fluid coking unit according to claim 3 in whichthe gasifier section includes a main gasifier vessel in which the solidparticles from the reactor with coke deposited on them are contactedwith the steam and oxygen-containing gas to form fuel gas and aseparator vessel having (i) a gas inlet connected to the main gasifiervessel, (ii) gas/solid filters for separating solid particles heated inthe main gasifier vessel from the fuel gas and (iii) a solid particlereturn line connecting the separator vessel to the main gasifier vesselfor returning separated solid particles to the main gasifier vessel.